The present invention relates in general to receiving techniques and more particularly to a quadrature output oscillator device.
Typically, quadrature outputs generated from voltage controlled oscillators are not ideal, i.e. the phase difference between the in-phase and quadrature-phase signal components are 90xc2x0xc2x1some error. The error in this phase difference is mostly due to device mismatch. However, many receiver topologies rely on precise quadrature in order to achieve frequency image rejection in the received signal. The quality of reception is degraded, in the presence of frequency images in the received signal, due to the imprecise quadrature component signal generation in the receiver. Frequency image rejection could be performed by passive filters, but these passive filters result in increased design complexities and higher costs. Therefore, it is desirable to have precise quadrature to achieve the desired receiver circuit performance.
From the foregoing, it may be appreciated that a need has arisen for a receiver that implements ideal in-phase and quadrature-phase signal components in order to effectively achieve proper frequency image rejection. In accordance with the present invention, a quadrature output oscillator device is provided that substantially eliminates or reduces disadvantages and problems associated with conventional quadrature output voltage controlled oscillator devices.
According to an embodiment of the present invention there is provided a quadrature output oscillator device that includes a first voltage controlled oscillator that generates a first output and a second output, wherein the second output of the first voltage controlled oscillator is an in-phase signal component. A second voltage controlled oscillator also generates a first output and a second output, wherein the second output of the second voltage controlled oscillator is a quadrature-phase signal component. A first amplifier receives the first and second outputs from the second voltage controlled oscillator. The first amplifier generates a first feedback signal coupled to the first output of the first voltage controlled oscillator and a second feedback signal coupled to the second output of the first voltage controlled oscillator. A second amplifier receives the first and second outputs from the first voltage controlled oscillator. The second amplifier generates a first feedback signal coupled to the first output of the second voltage controlled oscillator and a second feedback signal coupled to the second output of the second voltage controlled oscillator. A gain adjustment unit controls a gain of the first amplifier and the second amplifier in order to provide ideal in-phase and quadrature-phase signal components at the second output of the first voltage controlled oscillator and the second output of the second voltage controlled oscillator, respectively.
The present invention provides various technical advantages over conventional quadrature output voltage controlled oscillator devices. For example, one technical advantage is to provide ideal quadrature outputs from voltage controlled oscillators. Another technical advantage is to eliminate the use of passive filters in receiver topologies. Yet another technical advantage is in compensating for device mismatches within voltage controlled oscillators. Other technical advantages may be readily ascertainable by those skilled in the art from the following figures, description, and claims.